From d6e5c4325d1eb294e8f2df7d2761e987a504fe60 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Tue, 7 Jun 2022 22:25:31 -0400
Subject: [PATCH] Add new start rule ending with EOF token rather than
 appending EOF token to all user-specified start rules

---
 lib/propane/grammar.rb |  8 ++++++--
 lib/propane/parser.rb  | 14 ++++++--------
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/lib/propane/grammar.rb b/lib/propane/grammar.rb
index f14f230..cfdb673 100644
--- a/lib/propane/grammar.rb
+++ b/lib/propane/grammar.rb
@@ -35,7 +35,7 @@ class Propane
             pattern = name
           end
           unless name =~ /^[a-zA-Z_][a-zA-Z_0-9]*$/
-            raise Error.new("Invalid token name #{name}")
+            raise Error.new("Invalid token name #{name.inspect}")
           end
           @tokens << Token.new(name: name, pattern: pattern, id: @tokens.size, line_number: line_number)
         elsif sliced = input.slice!(/\Adrop\s+(\S+)\n/)
@@ -43,8 +43,12 @@ class Propane
           @drop_tokens << Token.new(pattern: pattern, line_number: line_number)
         elsif sliced = input.slice!(/\A(\S+)\s*->\s*(.*?)(?:;|<<\n(.*?)^>>\n)/m)
           rule_name, components, code = $1, $2, $3
+          unless rule_name =~ /^[a-zA-Z_][a-zA-Z_0-9]*$/
+            raise Error.new("Invalid rule name #{name.inspect}")
+          end
           components = components.strip.split(/\s+/)
-          @rules << Rule.new(rule_name, components, code, line_number, @rules.size)
+          # Reserve rule ID 0 for the "real" start rule.
+          @rules << Rule.new(rule_name, components, code, line_number, @rules.size + 1)
         else
           if input.size > 25
             input = input.slice(0..20) + "..."
diff --git a/lib/propane/parser.rb b/lib/propane/parser.rb
index 6149d37..829c39b 100644
--- a/lib/propane/parser.rb
+++ b/lib/propane/parser.rb
@@ -3,15 +3,13 @@ class Propane
   class Parser
 
     def initialize(start_rule_set)
-      @token_eof = Token.new(name: "$", id: TOKEN_EOF)
+      @eof_token = Token.new(name: "$", id: TOKEN_EOF)
+      start_rule = Rule.new("$$", [start_rule_set, @eof_token], nil, nil, 0)
       @item_sets = []
       @item_sets_set = {}
-      start_items = start_rule_set.rules.map do |rule|
-        rule.components << @token_eof
-        Item.new(rule, 0)
-      end
+      start_item = Item.new(start_rule, 0)
       eval_item_sets = Set.new
-      eval_item_sets << ItemSet.new(start_items)
+      eval_item_sets << ItemSet.new([start_item])
 
       while eval_item_sets.size > 0
         this_eval_item_sets = eval_item_sets
@@ -22,7 +20,7 @@ class Propane
             @item_sets << item_set
             @item_sets_set[item_set] = item_set
             item_set.following_symbols.each do |following_symbol|
-              unless following_symbol == @token_eof
+              unless following_symbol == @eof_token
                 following_set = item_set.build_following_item_set(following_symbol)
                 eval_item_sets << following_set
               end
@@ -71,7 +69,7 @@ class Propane
 
     def process_item_set(item_set)
       item_set.following_symbols.each do |following_symbol|
-        unless following_symbol == @token_eof
+        unless following_symbol == @eof_token
           following_set = @item_sets_set[item_set.build_following_item_set(following_symbol)]
           item_set.following_item_set[following_symbol] = following_set
           following_set.in_sets << item_set